1. Field of the Invention
The present invention generally relates to surveying, and more particularly to methods and devices for staking out boundaries or other features of a sports field such as field lines for a football field or soccer field.
2. Description of the Related Art
Sporting events that take place on a field or course with boundary lines or other demarcations must have accurate field measurements to ensure fair game play. Both players and spectators expect that the field lines for a competition will be perfect in geometry and dimensions. These requirements and expectations place a high burden on the field maintenance crew that must install boundary markers such as pegs or posts and paint markings on the field.
Current practice for sports field lining techniques requires considerable effort by field set up personnel to survey the field with measuring tapes, distance measuring wheels, theodolites or other equipment to locate various coordinates for each selected sport. Upright posts or flagged rods can be planted at these locations, or stakes can be inserted into the ground and a taut string tied between them to act as a guide for painting a stripe. Striping or other marks are then placed on the field indicating line positions or various surface point marking positions such as yard marking, hash marks, field centers, etc. The visual line marking points may be temporary or permanent, and can be used by line marking crews for visual referencing and by players and field judges for accurate refereeing.
Above-ground marking targets can present a hazard to players and so are often designed to be easily removed. One example of such a marking system is described in U.S. Pat. No. 5,186,119. Ground anchors are located at intersecting points of playing field lines, and the ground anchors are adapted to support various implements such as a peg having a spool of string, a numeric yard line marker, a flag pole, or a fence post. A soft marker pylon may also be supported by a flexible spring inserted into the ground anchor, so the pylon can bend under the impact of a player to avoid injury to the player or damage to the pylon, and thereafter spring back upright.
More complicated automated systems for sports field staking and marking are described in U.S. Pat. No. 6,330,503 and U.S. Patent Application No. 2005/0055142. The first of those inventions is directed to a vehicle running on autopilot which uses a global positioning system (GPS) receiver to locate the proper positions for driving stakes into the ground based on pre-programmed geographical coordinates. The second disclosure teaches an autonomous ground maintenance vehicle which applies field markings based on an X-Y coordinate system, and use of an infrared sensor to detect signals from reflective targets at known positions of the coordinate system and determine the location of the vehicle within the X-Y coordinate system.
One problem in the maintenance of field lines is that posts or stakes can be removed by play, weather or vandals, and the field must often be re-surveyed to re-locate the boundary reference points. This problem is reduced by the use of anchors which remain buried underground, but when there is no above-ground visual indicator affixed to the anchor it can become difficult to locate at a later time due to turf growth or soil movement. These problems are exacerbated for fields which are used for more than one sporting event, e.g., an outdoor stadium employed at different times for football and soccer. The posts marking different boundary reference points must be repeatedly removed and replaced, sometimes on a daily basis. Surveying equipment must be allocated to such fields permanently, and highly-trained field maintenance personnel must always be on hand, at least during the sporting season. Problems in relocating boundary markers for a second or third sport may cause a significant delay in the start of a game. Even if the reference points or ground anchors are all locatable, there may still be confusion about which points are to be used for the particular sport. It would, therefore, be desirable to devise an improved method and system for marking sports fields which could simplify the locating of boundary reference points, particularly for fields which are used with multiple sports. It would be further advantageous if relocation of the boundary points did not require complicated equipment or rigorous training of field personnel.